In the manufacture of printed circuit boards and cards a dielectric sheet material is employed as the substrate. A conductive circuit pattern is provided on one or both of the major surfaces of the substrate.
As described in, for instance, U.S. Pat. No. 3,689,991, and Tummala, "Microelectronics Packaging Handbook," pages 409-439, Van Nostrand Rhinehold, disclosures of which are incorporated herein by reference, flexible polymeric films can be used as carriers in the packaging of semiconductor chips such as in the so-called TAB (tape automated bonding) procedure. To date, the primary polymeric materials employed for such have been the polyimides.
The tape automated bonding technique involves bonding the tip ends of the leads formed in a selected pattern on a TAB tape to the electrodes of an IC chip via metallic bonding projections called bumps. In addition, solder bumps or balls may be used to connect the TAB tape to the connective pads on an integrated circuit board or card.
In order to handle the thin flexible film and protect it from damage during subsequent processing, TBGA films require a stiffener for support. Typically, the stiffener is constructed of metal, which is stamped so as to keep costs at a minimum. The stiffener is then attached using an adhesive to the thin flexible film layer. This attaching process however is somewhat costly. Moreover, some problems exist in handling the adhesive since such can absorb moisture which in turn can result in corrosion, "popcorning" or shorts between signal traces. Accordingly, there remains room for improvement in thin, flexible film technology.